Risks are everywhere. They come from many sources, including crime, diseases, accidents, terror, climate change, finance, and intimacy. They arise from our own acts and they are imposed on us. In this Very Short Introduction Fischhoff and Kadvany draw on both the sciences and humanities to show what all risks have in common. Do we care about losing money, health, reputation, or peace of mind? How much do we care about things happening now or in the future? To ourselves or to others? All risks require thinking hard about what matters to us before we make decisions about them based on past experience, scientific knowledge, and future uncertainties. Using conceptual frameworks such as decision theory and behavioural decision research, we examine the science and practice of creating measures of risk and look at how scientists apply probability by combining historical records, scientific theories, and expert judgement. Showing what science has learned about how people deal with risks, and applying these to diverse everyday examples, the authors demonstrate how we move from understanding a risk to making a choice in everyday life.